In recent years, there has been a demand from device manufacturers for an N-type low-resistivity crystal added with N-type dopant at a high concentration (N-type highly doped monocrystal) for application in a power MOSFET (metal oxide semiconductor field effect transistor) in order to reduce “On” resistivity.
However, when an N-type dopant is added at a high concentration as described above and an ingot is pulled up by Czochralski method, the freezing point is depressed to a considerably large degree due to the addition of the dopant in a large amount, so that compositional supercooling may be caused.
When such compositional supercooling is large, a growth different from a silicon growth face may be initiated on a crystal growth interface, which leads to an abnormal growth (cell growth). Occurrence of such an abnormal growth during a growing phase of an ingot may hamper the monocrystallization.
In view of the above, studies on such compositional supercooling have been conducted in a field of compound semiconductor such as GaAs, InP. According to a known technique, occurrence conditions of compositional supercooling are defined based on a relationship between a temperature gradient of the semiconductor melt and a pulling-up speed (e.g., patent document 1).
Patent Document 1: JP-A-61-31382